The present invention relates to circuits for controlling belt-driving. In particular, the present invention relates to a belt-drive-control circuit for controlling a belt-driving structure, such as a electrophotographic device, in which load varies greatly in late years.
Generally, a belt-driving mechanism comprises, as major components, a plurality of rollers, a belt mounted on the plurality of rollers, and a belt-driving motor for driving one roller among the plurality of rollers. A known belt-driving mechanism is controlled so as to rotate the roller at a predetermined constant speed. The belt is driven by the belt-driving motor in accordance with the load applied to the belt-driving mechanism. The belt thus driven receives an external load which varies at all times. The belt rollers receive the external load which varies depending on processes. For example, in a belt-driving mechanism used in an electrophotographic printer, the external load applied to the belt-driving mechanism by the component units, such as a developing unit and a transferring unit, varies depending on each process, such as a charging process, an exposing process, a developing process, a transferring process, or a cleaning process.
Therefore, the output of the belt-driving motor must be set to an optimal value quickly and accurately so as to control the rotation of the belt at a predetermined speed.
The flow of routines in a known circuit for controlling a belt-driving mechanism is described below. In a belt-driving routine, no external load is applied to the belt. In a developing-unit-driving routine, load is applied to the belt by development rollers. In a transfer-roller-driving routine, a maximum load is applied to the belt by a transfer roller and by the development rollers. In a known method for controlling a belt-driving motor, a servo constant and a servo parameter are set in a sequence of the belt-driving routine. The set values are those optimized for the maximum load. The operation in the known method is performed by using the optimized values in a servo-computing expression. However, the servo constant and the servo parameter are not set in the subsequent developing-unit-driving and transfer-roller-driving routines. By the known method, the control of rotation at a constant speed is possible in a servo system in which the difference in load between a maximum-load-state and the no-load-state is not significantly large.
However, in a colored electrophotographic printer in particular, the difference in load between a maximum-load-state and the no-load-state tends to increase due to enlarged component units of the printer and due to the printer being complex and increased in size. Therefore, a problem occurs in that complex and large-scale servo-computation expressions must be prepared for forming a software servo-mechanism, whereby a high-speed servo-controller must be provided for reducing computation processing time.
Accordingly, it is an object of the present invention to provide a belt-driving circuit for realizing a software servo-mechanism to be controlled at an optimal value in a device in which the external load applied to the belt varies greatly.
To the end, according to a first aspect of the present invention, a belt-drive-control circuit is provided, which controls a DC motor for driving the belt-driving mechanism including rollers and a belt mounted on the rollers by using a software servo-mechanism. The belt-drive-control circuit comprises a controller for controlling the DC motor by using servo constants and servo parameters variable in accordance with the variation in the load applied to the belt.
With this arrangement, the belt-driving mechanism and the units connected thereto can be driven by the DC motor with accuracy, even when variation in the load applied to the belt occurs, by controlling the DC motor in accordance with servo constant and servo parameter optimal for a particular loaded state of the belt. The control is possible by providing a control method in which the servo constant and the servo parameter are variable in accordance with the load applied to the belts. In the belt-drive-control circuit, computation processes can be proceeded easily because it is not necessary to modify known computation expressions for a software servo-mechanical control. Therefore, the driving accuracy can be maintained at a high level without upgrading a computing device.
In the belt-drive-control circuit according to the present invention, the controller comprises a memory unit and a computing unit. The memory unit stores data on the load applied to the belt and a plurality of sets of the servo constants and the servo parameters. The computing unit receives the data on the load applied to the belt from a central processing unit. Then, the computing unit reads from the memory unit the servo constant and the servo parameter in accordance with the received data on the load applied to the belt, performs a servo-computation by using the read servo constant and servo parameter, and computing rotational-speed data.
According to a second aspect of the present invention, an electrophotographic device comprises a photosensitive belt, a DC motor, a plurality of rollers, a central processing unit, and a belt-drive-control circuit according to the first aspect of the present invention. The DC motor drives the photosensitive belt. The plurality of rollers may be individually come into contact with and separate from the photosensitive belt at the peripheries of the rollers. The central processing unit controls the entire operation of the electrophotographic device including the movement of the plurality of rollers toward and away from the photosensitive belt. The belt-drive-control circuit controls the DC motor by using a software servo-mechanism. The central processing unit computes load data on the photosensitive belt in each driving process in which load varies between each process in accordance with the number of the rollers in contact with the photosensitive belt at the peripheries of the rollers. The central processing unit enables to send the load data to the belt-drive-control circuit.
The electrophotographic device according to the present invention has an advantage due to the above-described belt-drive-control circuit in that a belt-driving mechanism and units included in the belt-driving mechanism can be driven with accuracy regardless of a process proceeded electrophotographically. For example, the process are such as a charging process, an exposure process, a developing process, a transferring process, or a cleaning process, thereby improving the quality of electrophotography.